Wall construction for pressurized furnace



Jun 6, 1961 w. H. ARMACOST WALL CONSTRUCTION FOR PRESSURIZED FURNACEOriginal Filed 001:. 29, 1952 5 Sheets-Sheet 1 INVENTOR. WILBUR H.ARMACOST E L Egg I igi 58 I INVENTQR WILBUR H. ARMACOST June 6, 1961 w.H. ARMACOST 2,987,052

WALL CONSTRUCTION FOR PRESSURIZED FURNACE Fig. 2.

Fig. 3. BY g ATTOR Y June 6, 1961 w. H. ARMACOST WALL CONSTRUCTION FORPRESSURIZED FURNACE Original Filed Oct. 29, 1952 3 Sheets-Sheet I5 Fig.6.

Fig. 5.

lNV ENTOR WILBUR H. ARMACOST BY Qffi-fi d ATTOR United States Patent C2,987,052 WALL CONSTRUCTION FOR PRESSURIZED FURNACE Wilbur H. Armacost,Scarsdale, N.Y., assignor to Combustion Engineers, Inc., a corporationof Delaware Continuation of application Ser. No. 317,520, Oct. 29, 1952.This application Sept. 29, 1958, Ser. No.

6 Claims. (Cl. 122-6) My invention relates to a method of fabricatingfurnace walls and has specific reference to a water cooled furnace wallof novel pressure resistant design especially adapted for use in thefurnace of a controlled circulation steam generator.

In the steam generation field there are two well known types of draftsystems employed by boiler designers today, i.e., the forced draftsystem and the induced draft system. In the forced draft system thecombustion supporting air is pumped into the furnace atsuper-atmospheric pressure while in the induced draft system thepressure within the furnace is reduced to below atmospheric so that theair is drawn into the furnace. Thus in both of these systems there is adifferential between the pressure within the furnace and the pressureexteriorly of the furnace, this differential being sufiicient whenacting on the large wall area of the furnace to exert a considerableforce on the furnace walls tending to collapse or push the sameoutwardly. With the tremendously high pressure prevailing within thesteam generating tubes of modern steam generators of the utility type itis indeed a challenging problem to fabricate for the furnaces of thesegenerators an economically feasible furnace wall that is lined with saidsteam generating tubes and is capable of withstanding the aforementionedforce.

' It is the general object of my invention to provide a method offabricating such a furnace wall.

A more specific object is to provide a method of fabricating a pressureresistant furnace wall having the inner surface lined with integrallywelded steam generating tubes with the outer structure of the wallsupported only indirectly from said tubes. A further object is toprovide an improved method of fabricating a pressure resistant furnacewall having the inner surface lined with spaced steam generating tubeswith the outer structure of the wall supported from spacer memberspositioned intermediate and welded to said tubes.

Other and further objects of my invention will become apparent to thoseskilled in the art as the description hereof proceeds.

With the aforementioned objects in view my invention comprises anarrangement, construction and combination of the elements of the furnacewall organized in such a manner as to attain the results desired ashereafter more particularly set forth in the following detaileddescription of an illustrative embodiment; said embodiment being shownby the accompanying drawings wherein:

FIG. 1 is a vertical section of a modern controlled circulation steamgenerator having a forced draft furnace the walls of which areconstructed in accordance with my invention;

. FIG. 2 is a sectional view of the furnace wall taken generally alongline 2-2 of FIG. 1.

FIG. 3 is a perspective view of a portion of said furnace wall showingthe construction details thereof.

FIG. 4 is an enlarged horizontal sectional view of a portion of saidfurnace wall being taken generally along the same line 2-2 as FIG. 2.

FIG. 5 is a vertical section taken generally along line 55 of FIG. 4.

FIG. 6 is a vertical section taken generally along line 6-6 of FIG. 4.

FIG. 7 is a sectional view similar to FIG. 4 but showing a modified formof construction.

While my furnace wall is herein shown and described as incorporated in acontrolled circulation boiler of particular design it is to beunderstood that this is illustrative only and is not to be taken asrestrictive since as the description proceeds it will become apparentthat my in-. vention may be equally well employed with boilers of otherand different designs.

By the term controlled circulation, as used throughout this application,is meant a steam generator having a positive or forced circulationthrough the various steam generating tubes and provided with restrictingorifices dis posed adjacent the inlets of such tubes and so designed asto control the flow therethrough in a predetermined manner to obtainmaximum boiler efficiency.

The steam generator here illustrated Referring specifically to thedrawings wherein like reference characters are employed throughout todesignate like elements, the steam generator of FIG. 1 com prises avertically disposed furnace 2 of generally rec'- tangular cross sectioncommunicating at its upper end with a horizontal gas pass 4 which inturn communicates with the upper end of vertical gas pass 6 leading toair preheater 14. A plurality of vertically spaced burners 8 communicatewith the interior of said furnace and are arranged to supply theretopulverized coal received from pulverizers 10 via conduits 12. Preheatedair is introduced into the furnace under pressure via a suitable forceddraft fan (not shown) which forces the air through the preheater 14 andduct 16 from whence it is introduced into the furnace at a plurality ofvertically spaced points, such introduction insuring complete burning ofthe fuel passed into the furnace by said burners.

Furnace 2 is of the water cooled type having the interior surface of itswalls as well as the floor and ceiling lined with steam generating tubes18. Said tubes 18 are connected at their lower or inlet ends withorifice drum 20 and at their upper or outlet ends with conventionalheaders 22 which in turn communicate with steam and water drum 24through conduits 23. Downcomers 25 (only one being shown) extend downfrom steam and water drum 24 and communicate at their lower ends withthe inlet of pumps 26 (again only one being shown) which in turn havetheir outlets connected by suitable conduits 28 to orifice drum 20thereby completing a fluid circuit through which said pumps areeffective to circulate boiler water in a direction indicated by thearrows in FIG. 1. Suitable fiow restrictors in the form of orifices (notshown) of predetermined size are associated with the inlet of each ofthe tubes 18 for the purpose of effectively controlling the flow througheach of said tubes.

Disposed within gas passes '4 and 6, respectively, are a plurality ofheat exchange devices; namely, high temperature superheater 32, reheater34, low temperature superheater 30 and economizer 29, which are arrangedThe construction of the furnace wall Referring specifically to FIGS. 2to 6, inclusive, each of the water evaporating tubes 18 which, aspreviously noted, line the interior of furnace 2, is spaced apredetermined distance from its adjacent tubes with the spacestherebetween being substantially filled by metallic rods 36, preferablycircular in cross section, extending throughout the entire length of thetubes. Said rods 36 are welded to the tubes between which they aredisposed with weld metal completely surrounding said rods throughouttheir entire length thereby forming an extremely rigid, gas impervious,pressure resistant metallic interior surface for said furnace wall.

At predetermined vertically spaced intervals, suitable outwardlyprojecting studs 38, in the form ,ofrectang'ular plates, are welded tovarious of said rods 36 in the inanner best shown by Figs. 3 and 4.Horizontally disposed channel stiffener and support members 40 arepositioned between and welded to such studs 3d and have, at horizontallyspaced intervals, suitable gusset plates 42 welded thereto. To the outerextremity of said gusset plates 42 are welded two spaced horseshoefasteners 44 having their centrally disposed openings in alignment andgenerally parallel with the axis of tubes 18, said aligned openingsloosely receiving flanges 46 of buckstay 48 in order to support thebuckstay from the wall while allowing relative movement therebetween dueto. unequal expansion.

The surface of integrallyvwelded tubes 18 remote from the inner surfaceof the furnace wall is lined with suitable thermal insulation in theform of an inner row of insulating blocks 50, an outer row of insulatingblocks 52 and a layer of plastic insulation 54. All of the insulation issupported solely by studs 38 and channel members 40 and since the innersurface of the furnace wall is a gas tight, pressure resistant, metallicstructure no outer metallic casing is necessary.

Heretofore it has been the practice to provide pressurized furnace wallswith an outer metallic casing, genorally in the form of sheet steel, inorder to retain various packing material in place and thereby maintainsaid walls substantially fluid tight. However, since the wall of myinvention presents an inner metallic surface which in itself isimpervious to fluid the need for the outer casing is eliminatedresulting in a significant saving of material and labor.

In controlled circulation boilers it is possible to rigidly weldtogether the steam generating tubes lining the furnace wall along theirentire length as herein disclosed. This is due to the fact that apositive circulation of the boiler water substantially eliminates hotspots within the furnace which are the cause of excessive differentialexpansion. Integrally welding the steam generating tubes of a naturalcirculation boiler in this manner is, on the contrary, extremelyimpracticable since upon initially firing such a boiler there is nocirculation of water through the steam generating tubes and consequentlyportions of said tubes become extremely hot while other portions remainrelatively cool. This results in excessive dilferential expansionsetting up intolerable strains within such a welded wall. It is thusseen that my novel wall construction is particularly well adapted foruse with steam generators having a forced circulation and especially thecontrolled circulation type since by providing a positive flow of waterthrough each tube the chance for hot spots is substantially eliminated.

In fabricating the welded wall herein disclosed in FIGS. 2 to 6 it ispracticable (and is actually being carried out by my assignee) to weldthe tubes into large panels at the shop and ship these panels to thefield. Thus during erection in the field it ismerely necessary to weldthese ass /pea various panels together thereby reducing the number offield welds to a minimum.

All of the welds, i.e., the longitudinal welds joining the tubestogether, are stress relieved whereby, in accordance with the ASME code,they have little effect upon the strength quality of the tube. With theequipment available at the fabrication shops it is a simple andrelatively inexpensive matter to stress relieve these welds and sincethe few welds made in the field extend longitudinally throughout thelength of the panels they may also be economically stress relieved.

Any weld applied directly to the surface of a stream generating tube andnot stress relieved has the effect of greatly decreasing the strengthquality of the tube and setting up excessive stresses in the tube wallat the loca-- tion of the weld. Thus when support studs for insulationand other wall structure are welded directly to thetubes and not stressrelieved, as is common practice in conventional furnace walls, it leavesthe tubes in a weakened condition at the location of said weld. Tostress relieve the many and scattered support studs required isprohibitively expensive and thus in said conventional furnace walls thetubes are left with these locations of weakness which areever presentpotential sources of failure.

With my novel wall structure herein disclosed in FIGS. 2 to 6 thisundesirable feature is completely eliminated by welding the support lugsto rods 36 disposed between the tubes. This weld has no elfect upon thetubes and since as pointed out above, all of the welds applied directlyto the tubes in my novel wall can economically be stress relieved, thetube' is left entirely free of excessive stresses and locations where itis relatively weak.

The modification of FIG. 7 is similar to the embodiment of FIGS. 2 to 6except that in lieu of spacer rods 36 tubes 118 are formed throughouttheir length with the diametrically opposed laterally extendingextrusions 120 with the edges of adjacent extrusions being immedi' atelyadjacent one another or in engagement so that the tube proper ofadjacent tubes are in spaced relation with this space being filled withmetal. These edges are welded together throughout their length thusforming, as in the case of the previously described embodiment, anextremely rigid, gas impervious, pressure resistant metallic interiorsurface for the furnace wall.

Welded to said extrusions 120 intermediate certain of said tubes and atpredetermined vertically spaced intervals are outwardly projecting studs38. Said studs 38 support the outer structure of the wall in the samemanner as the. previously described embodiment and the details thereofwill not be repeated here.

In fabricating the wall of this embodiment of my invention the tubes mayalso be welded into large panels and stress relieved in the shop therebyreducing the welding and stress relieving required in the field.Although the welding together of these tubes does not weaken them to theextent of the tubes in the previously described embodiment, due to thefact that the weld is more remote from the tube wall, it is stilladvisable to stress relieve this weld because of the resulting warpingif not stress relieved and because this large weld does somewhat weakenthe tubes. The relatively small welds required to secure studs 38 to theextrusions at a point intermediate adjacent tubes have no effect on thestrength quality of the tubes, however, whereby an extremely practical.and highly desirable pressure resistant wall is produced which requiresno separate casing.

Summary From the foregoing. it will be seen that I have provided animproved method of fabricating a water cooled pressure resistant wallparticularly adapted for furnaces of controlled circulation boilers withthe wall having an inner surface of rigidly welded heat exchange tubespresenting an imperforate metallic inner face and provided with supportstuds welded intermediate said tubes and arranged to support the outerwall structure. a

"aesaoaa While I have' illustrated and described a preferred embodimentof my novel furnace wall it is to be understood that such is merelyillustrative and not restrictive and that variations and modificationsmay be made therein without departing from the spirit and scope of theinvention. I therefore do not wish to be limited to the precise detailsset forth but desire to avail myself of such changes and alterations asfall within the purview of my invention.

This application is a continuation of my application Serial No. 317,520,filed October 29, 1952, now abandoned.

What I claim is:

l. The method of constructing a furnace wall which has its inner surfacelined with heat exchange tubes constructed and arranged to form a rigid,imperforate metal lic inner face for the wall with the outer portions ofthe wall being supported from this rigid inner face, comprising thesteps of shop assembling panels of parallel tubes by maintaining thetubes in parallel relation with the wall portion of adjacent tubes whichis defined as being of uniform thickness perimetrically of the tube andcontiguous to and in bounding relation with the passage through the tubebeing spaced with this wall portion comprising the entire thickness ofthe tube wall throughout at least a portion of the tube perimeter,providing metal in said space substantially filling the same, weldingadjacent tubes together throughout their length, shop stress relievingthese panels after this welding, assembling these panels in the field toform an imperforate metallic inner wall face by maintaining the edgetubes of adjacent panels in parallel spaced relation and interconnectingthe same throughout their length by welding, stress relieving thesewelds, supporting stiffener members from this inner face on the outerside thereof by positioning support lugs principally in engagement withthe metal intermediate the tubes and welding said support lugssubstantially solely to this metal in a manner so as to have noappreciable eifect upon the strength quality of the tubes with thiswelded joint being the sole connecjtfion of these lugs with thisimperforate metallic inner ace.

2. The method of constructing a furnace wall made up of a plurality oflayers and which has a layer of parallel tubes formed into a fluidimpervious pressure resistant structure from which other portions of thewall are supported comprising shop assembling panels of said tubes bymaintaining the tubes in parallel relation, with the wall portion ofadjacent tubes which is defined as being of uniform thicknessperimetrically of the tube and contiguous to and in bounding relationwith the passage through the tube being spaced with this wall portioncomprising the entire thickness of the tube wall throughout at least aportion of the tube perimeter, providing metal in said spacesubstantially filling the same throughout the length of the tubes,welding the adjacent tubes of the panels together throughout theirlength and shop stress relieving these welds, assembling these panels inthe field to form an imperforate metallic layer of a furnace wall withthe tubes of the panels being free of any substantial stresses,positioning support lugs principally in engagement with the metalintermediate the tubes and welding said support lugs substantiallysolely to this metal in a manner so as to have no appreciable efiectupon the strength quality of the tubes and so these lugs extendlaterally of the imperforate metallic layer formed by the tubes and withthis welded joint being the sole connection of these lugs with thisimperforate metallic layer, with these lugs being adapted to supportother structure.

3. The method of fabricating a furnace wall made up of a plurality oflayers and which has its inner surface lined with heat exchange tubesconstructed and arranged to form a rigid, imperforate metallic innerface for the wall with the outer portions of the wall being supportedfrom this rigid inner face, comprising the steps of main? taining thetubes in parallel relation with the wall poi-tion of adjacent tubeswhich is defined as being of uniform thickness perimetrically of thetube and contiguous to and in bounding relation with the passage throughthe tube being spaced with this wall portion comprising the entirethickness of the tube wall throughout at least a portion of the tubeperimeter, providing metal in said space substantially filling the same,welding adjacent tubes together throughout their length, stressrelieving these welds, positioning support lugs principally inengagement with the metal intermediate the tubes and, welding saidsupport lugs substantially solely to this metal in a manner so as tohave no appreciable efiect upon the strength quality of the tubes andwith this welded joint being the sole connection of these lugs with thisimperforate metallic inner face, these lugs being adapted to supportother structure.

4. The method of constructinga furnace wall made up of a plurality oflayers and which has its inner surface lined with heat exchange tubesconstructed and arranged to form a rigid, imperforate metallic innerface for the wall with the outer portions of the wall being supportedfrom this rigid inner face, comprising the steps of shop assemblingpanels of parallel spaced tubes by interposing metallic spacer rodsbetween adjacent tubes throughout their length, shop welding these tubestogether throughout their length and across said rods shop stressrelieving these panels after this welding, assembling these panels inthe field to form an i rnperforate metallic inner wall face with thetubes of the panels being free of any substantial stresses, positioningsupport lugs principally in engagement with the metal intermediate thetubes and welding said support lugs substantially solely to this metalin a manner so as to have no appreciable effect upon the strengthquality of the tubes, and with this welded joint being the soleconnection of these lugs with this imperforate metallic inner face,these lugs being adapted to support other structure.

5. The method of constructing a furnace wall made up of a plurality oflayers and which has its inner surface lined with metallic heat exchangetubes which are provided with generally diametrically opposed,longitudinally extending fins with these tubes being constructed andarranged to form a rigid, imperforate metallic inner face for the wallwith the outer portions of the wall being supported fro-m this rigidinner face, comprising the steps of shop assembling panels of paralleltubes by positioning the same with the edges of their fins juxtaposedand weld ing these edges together throughout the length of the tube,shop stress relieving these panels after this welding, assembling thesepanels in the field to form an imperforate metallic inner wall face withthe tubes of the panels being free of any substantial stresses,positioning support lugs principally in engagement with the metalintermediate the tube proper of adjacent tubes and welding said supportlugs substantially solely to this metal in a manner so as to have noappreciable effect upon the strength quality of the tubes and with thiswelded joint being the sole connection of these lugs with thisimperforate metallic inner face, these lugs being adapted to supportother structure.

6. The method of fabricating a furnace wall which is made up of aplurality of layers one of which is heat exchange tubes rigidly securedtogether into a metallic layer comprising the steps of maintaining thetubes in parallel relation with the wall portion of adjacent tubes whichis defined as being of uniform thickness permetrically of the tube andcontiguous to and in bounding relation with the passage through the tubebeing spaced with this wall portion comprising the entire thickness ofthe tube wall tthroughout at least a portion of the tube perimeter,providing metal in said space substantially filling the same, weldingadjacent tubes together throughout their length, stress relieving thesewelds, positioning References Cited in the ;fi1eof this patent UNITEDSTATES PATENTS Murray et a1 Now. 30, 1926 Jacobus May 22,1234 Inskeep eta1 Sept. 22,, 1942 Witzke May 15, 1951 Har dgrove Apr. 5,, 1955

